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Title: A laboratory nanoseismological study on deep-focus earthquake micromechanics

Global earthquake occurring rate displays an exponential decay down to ~300 km and then peaks around 550 to 600 km before terminating abruptly near 700 km. How fractures initiate, nucleate, and propagate at these depths remains one of the greatest puzzles in earth science, as increasing pressure inhibits fracture propagation. We report nanoseismological analysis on high-resolution acoustic emission (AE) records obtained during ruptures triggered by partial transformation from olivine to spinel in Mg 2GeO 4, an analog to the dominant mineral (Mg,Fe) 2SiO 4 olivine in the upper mantle, using state-of-the-art seismological techniques, in the laboratory. AEs’ focal mechanisms, as well as their distribution in both space and time during deformation, are carefully analyzed. Microstructure analysis shows that AEs are produced by the dynamic propagation of shear bands consisting of nanograined spinel. These nanoshear bands have a near constant thickness (~100 nm) but varying lengths and self-organize during deformation. This precursory seismic process leads to ultimate macroscopic failure of the samples. Several source parameters of AE events were extracted from the recorded waveforms, allowing close tracking of event initiation, clustering, and propagation throughout the deformation/transformation process. AEs follow the Gutenberg-Richter statistics with a well-defined b value of 1.5 over threemore » orders of moment magnitudes, suggesting that laboratory failure processes are self-affine. The seismic relation between magnitude and rupture area correctly predicts AE magnitude at millimeter scales. A rupture propagation model based on strain localization theory is proposed. Future numerical analyses may help resolve scaling issues between laboratory AE events and deep-focus earthquakes.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [1] ;  [1] ;  [1] ;  [5] ;  [4] ;  [2] ;  [6]
  1. Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources
  2. St. Louis University, MO (United States). Department of Earth and Atmospheric Sciences
  3. China University of Geosciences, Wuhan (China). State Key Laboratory of Geological Processes and Mineral Resource; Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources
  4. PSL Research University, Paris (France). Laboratoire de Geologie, Ecole Normale Superieure
  5. Universite de Lille (France). UMET -Unite Materiaux et Transformations
  6. Universite Grenoble Alpes (France)
Publication Date:
Grant/Contract Number:
FG02-94ER14466; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Science Advances
Additional Journal Information:
Journal Volume: 3; Journal Issue: 7; Journal ID: ISSN 2375-2548
Publisher:
AAAS
Research Org:
Univ. of Chicago, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1424023